A fairly inexpensive entry to a walking GPS is a
SatMap Active 10
Chosen by 40+ UK rescue teams so must be 'reasonable'.
http://cdn.satmap.com.s3-eu-west-1.amazonaws.com/A10%20leaflet%20english.pdfMany available on ebay and reach about £70, with some buy it now at £100 The 'cards' they come with make a big difference in price.
Mine (£70 second hand, about £300 new) came with full GB 1:50,000 Ordnance Survey mapping, ( which is the scale I use on the 'paper maps')
I have subsequently purchased a separate 'card' with 'South UK (Liverpool across to Hull and all points South) at a scale of 1:25,000 and 1:10,000 and the difference is amazing.
Simple to use with big buttons operable with gloves on.
Battery lasts 15 hours and in an emergency can be run on 3x AA batteries.
After 50+ years of paper maps and compass I found the whole GPS thing a minefield with so many brands and models, most of which need additional mapping (extra ££££££s) The SatMap Active is really usable straight from the box.
You can plan routes and save them, save routes you have done to memory, do 'reverse' so if lost press 'reverse' and it takes you back the way to came.
You can download routes from the internet and SatMap website.
Screen size is (to me) important and the Garmin Etrex family all seemed too small. I would have liked a bigger screen than the SatMap 10 but everything is a compromise.
The Garmin Etrex has a 2" screen, the Satmap 10 has a 3.5" screen
Here is an example on ebay which has the 1:50,000 OS mapping
https://www.ebay.co.uk/itm/112940786402?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649WHATEVER YOU DECIDE TO BUY - CHECK OUT WHAT MAP SOFTWARE IT COMES WITH, HOW 'USABLE' IS IT AND THE COST OF BUYING 'USABLE' MAPS.
Some of the GPS systems come with 'open street map' which is a fairly poor standard of mapping with all sorts of problems for walker, with footpaths not shown or disappearing part way along, or showing footpaths where non exist. The system only becomes 'usable' with the purchase of additional mapping.
Do some research and don't rush in.